Thanks very much for taking the trouble to reply. It is a feature of this website that periodically people will refer to themselves as having superior ears to the ears of those disagreeing with them, and I was hoping we might get a glimpse into the reasoning behind this phenomenon. However, as all is silent from those prone to such claims, I can only guess that such beings might be owls, elephants, jackals or perhaps even deities...In any case, I'll offer my opinions...
1/ Healthy, clean, youthful.
2/ In the interests of this thread I took several online hearing tests. The results would only be of any use if you had some sort of serious problem - one test even reported that could hear up to 22khz - not bad for a 40 year old human. In any case, I seem to be healthy enough. How long it would take me to notice were my partner to mischievously swap the odd interconnect? I don't know...maybe never!
The way the brain processes information from the ears is vastly complex, and it will play incredible tricks on us. Many such tricks are exploited for our pleasure and convenience, such as harmonic exciters in the recording process, MP3s compressing huge amount of data, speakers seeming to throw sound forward and many, many more. Other tricks are less desirable, but we are all prone to them. The idea that we hear simply "what is there" is quite simply wrong.
3/ It is very rare that a lack of information would give a person an increased insight into a subject, and perhaps realistic expectations might increase their enjoyment...